It is already known, in order to dry compressed gas, to make use of a dryer having at least two pressure vessels which are filled with a desiccant or drying agent, which pressure vessels work alternately, such that when one pressure vessel is in action to dry the compressed gas, the other pressure vessel is being regenerated, whereby, in order to dry the compressed gas, this gas is first cooled in a cooler and is then sent through the drying pressure vessel and whereby, in order to regenerate the other pressure vessel, at least a part of this compressed gas is guided counterflow through the regenerating pressure vessel.
Also, it is already known to use, at the end of the regeneration cycle of the regenerating pressure vessel, a part of the compressed gas to cool the regenerated or almost regenerated drying agent by making this part of the compressed gas expand to the atmospheric pressure first, whereby this expanded gas, after its passage through the regenerating pressure vessel, is blown off in the atmosphere.
An advantage of cooling the drying agent in the regenerating pressure vessel at the end of the regeneration cycle is that, at the time the pressure vessels switch over, whereby the regenerated pressure vessel becomes drying pressure vessel and vice versa, temperature and dew point peaks of the compressed gas are avoided.
A disadvantage of this known method, however, is that relatively large amounts of compressed air are lost in the atmosphere and that blowing off already compressed air to an atmospheric pressure entails large energy losses, which may lead to considerable extra costs in the case of a compressor device with a large capacity.